Bringing cellular-level detail to an established clinical imaging approach could shed light on disease mechanisms.

To see the retinas of people with vision-related diseases like macular degeneration and retinitis pigmentosa, doctors routinely use a noninvasive imaging technique called infrared autofluorescence, or IRAF. IRAF can detect fluorescent light naturally emitted by a layer of cells called retinal pigment epithelial or "RPE" cells, which play essential roles in maintaining the overall health of the retina. However, conventional IRAF instruments don’t have high enough resolution to discern cellular details.

In a study published Sept. 7 in the journal Biomedical Optics Express, Johnny Tam and his colleagues at the National Eye Institute in Bethesda, Maryland, demonstrated that the combination of adaptive optics, or AO, with IRAF—or "AO-IRAF" for short—enables higher-resolution imaging, linking the cellular world with the macroscopic clinical picture.

AO is a technology that was originally developed by astronomers to sharpen images by compensating for blur-inducing optical aberrations caused by turbulence within the earth's atmosphere. In the field of vision science, AO compensates for the optical imperfections of the eye, allowing the visualization of individual retinal cells in ways not possible before.

For example, in a previous study, Tam and his colleagues recently reported that AO-IRAF can resolve individual RPE cells. But that study did not address whether AO-IRAF could be used to quantify the density of RPE cells at various locations in the retina for future comparisons to measurements from diseased eyes.

To answer that question, the researchers further modified a custom-built adaptive optics scanning light ophthalmoscope to improve the detection of fluorescent light emitted by RPE cells. Using this modified AO-IRAF instrument, they quantified the density of RPE cells at various locations in the retinas of 10 healthy subjects. Moreover, AO-IRAF images from a patient with retinitis pigmentosa showed a clear improvement in resolution compared with conventional IRAF images.

According to the authors, AO-IRAF brings cellular-level detail to an established clinical imaging modality, letting researchers zoom in on the microscopic changes that contribute to disease.